Add supported commands in server capabilities (#11850)
## Summary
This PR updates the server capabilities to include the commands that
Ruff supports. This is similar to how there's a list of possible code
actions supported by the server.
I noticed this when I was trying to find whether Helix supported
workspace commands or not based on Jane's comment
(https://github.com/astral-sh/ruff/pull/11831#discussion_r1634984921)
and I found the `:lsp-workspace-command` in the editor but it didn't
show up anything in the picker.
So, I looked at the implementation in Helix
(https://github.com/helix-editor/helix/blob/9c479e6d2de3bca9dec304f9182cee2b1c0ad766/helix-term/src/commands/typed.rs#L1372-L1384)
which made me realize that Ruff doesn't provide this in its
capabilities. Currently, this does require `ruff` to be first in the
list of language servers in the user config but that should be resolved
by https://github.com/helix-editor/helix/pull/10176. So, the following
config should work:
```toml
[[language]]
name = "python"
# Ruff should come first until https://github.com/helix-editor/helix/pull/10176 is released
language-servers = ["ruff", "pyright"]
```
## Test Plan
1. Neovim's server capabilities output should include the supported
commands:
```
executeCommandProvider = {
commands = { "ruff.applyFormat", "ruff.applyAutofix", "ruff.applyOrganizeImports", "ruff.printDebugInformation" },
workDoneProgress = false
},
```
2. Helix should now display the commands to pick from when
`:lsp-workspace-command` is invoked:
<img width="832" alt="Screenshot 2024-06-13 at 08 47 14"
src="https://github.com/astral-sh/ruff/assets/67177269/09048ecd-c974-4e09-ab56-9482ff3d780b">
